Could you clarify what exactly your goal would be? For example, are you wishing to argue against a contraceptive mentality or trying to promote NFP? Or both? Or something else?
I think the former is much more difficult to argue without discussing Christian viewpoints. Unfortunately, the fact is that in our society, people have grown accustomed to separating marital relations from the possible fruits of this intimacy. Even married couples are, at times, fearful of conceiving, and it can be difficult to convince people to cede control (or what they perceive is control).
For the latter goal (i.e., promotion of NFP), I think issues of side effects from contraceptive methods are becoming an increasing concern for women. I certainly find this to be true from anecdotal experience from conversations with numerous women, and there might well be studies to back that up. If women are made aware that there is an effective alternative to their current contraceptive method, they might be more likely to switch family planning methods. For many woman, side effects like mood swings or abnormal bleeding are not insignificant. Sure, all drugs can have side effects, but here there is an alternative.
And nowadays, many people are moving toward a more “natural” lifestyle–everything from eating organically to avoiding drugs unless necessary. There are certainly people who prefer to let their bodies work like they are supposed to.
Expense and convenience are other issues. The great thing about NFP is that it can be very cheap and always available–especially if resources for NFP instruction can be made more readily available and made appropriate for a a more widespread audience.
Many women (again, anecdotally speaking) feel very empowered when they learn NFP. Just go over to the Fertility Friend or Ovusoft boards to see how many women wish they had had such great knowledge about their bodies years ago.
Also, I wanted to give a word of caution about comparing effectiveness rates. I have noticed a tendency among NFP advocates to cherry pick the rates that make their point, whether intentional or not. (Whether or not promoters of contraceptives do so is not the issue here, in my opinion. We need to be as honest and up front as possible.) The fact is that one needs to be careful when comparing rates and studies. If you’re interested in learning more, I’d recommend looking up articles by Robert Kambic. Here is one where he discusses NFP effectiveness:
usccb.org/prolife/issues/nfp/cmrwin00.shtml
My dilemma is always how to promote NFP, knowing that for many people, it will simply replace their contraceptive method. I suppose that at least it will limit the abortions that occur as a result of contraception. And I think that NFP can foster communication in a marriage and help change a couple’s mentality.
Anyway, I’m rambling now. I hope this helps a little. (And although I’ve been reading here for years, this is my first post. So please be gentle.

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